1. Field of the Invention
The present invention relates to an impact-absorbing member for vehicles, which is suitable for use in a car bumper, for absorbing impact during a collision in order to avoid personal injury.
2. Description of the Related Art
To date, impact-absorbing members of various kinds have been employed in vehicle body frames, for the purpose of absorbing impact during a collision in order to avoid personal injury. For example, bumpers for absorbing impact energy during an automobile collision are attached to the front and rear of the vehicle body frame. Such bumpers are typically composed of metallic crush boxes attached with screws or the like to the vehicle body frame, a metallic bumper beam mounted to the outside of the crush boxes, and a resin bumper fascia attached to the outside of the bumper beam.
During a mild collision occurring at low speed, a bumper of this kind will absorb the impact energy by means of elastic deformation of the pliable resin bumper fascia as it softly bumps against the impacted object. This can reduce the extent of damage to the impacted object, and can prevent injury to a pedestrian or the like. However, in order to prevent damage to the impacted object, the bumper fascia must undergo a sufficient level of elastic deformation, and a correspondingly large deformation space for the bumper fascia is required.
During a strong collision such as a high-speed collision between automobiles or a vehicle with a structural object, the large impact energy is absorbed through plastic deformation and collapse of the steel bumper beam and crush boxes. This can reduce the extent of damage to the vehicle body and injury to occupants. The bumper beam and crush boxes are typically fabricated of metal such as steel or aluminum based materials, and thus in order to avoid increased weight, are designed with a hollow structure having a hollow section in the interior. In order to improve the strength of the bumper beam, there have been employed various methods such as adding a reinforcing plate as taught in JP-A-6-171441, making the metal plate which forms the bumper beam thicker, or filling the hollow section in the bumper beam with an expanded elastomer such as expanded urethane or the like, as taught in JP-A-2001-132787.
In recent years, higher levels of pedestrian safety in the event that a pedestrian is hit have come to be required, and higher impact energy absorbing ability is now required in particular for bumpers with high risk of hitting pedestrians.
To meet this requirement, there has been proposed an energy absorbing member for personal safety use, which is designed to be able to produce deformation in the cross sectional direction necessary to absorb energy at low impact load comparable to hitting a person, as taught in JP-A-2004-90910. This energy absorbing member is composed of a front face flange and a rear face flange disposed substantially parallel to one another in the front/back direction of the vehicle body, and left and right webs connecting these flanges and disposed substantially parallel to one another. Each web comprises a hollow material of aluminum alloy which bows towards the outside. However, since this energy absorbing member is fabricated of hollow aluminum alloy, it will tend to have higher weight as compared to resin materials, which represents a disadvantage in terms of fuel consumption.
Also as impact-absorbing members for absorbing impact energy when relatively low impact load is input, there are known in the prior art to date molded articles of prescribed shape formed from resin materials. These impact-absorbing members fall into two broad classes.
One of these is expanded elastomers such as expanded urethane and expanded PP (polypropylene), used to fill the hollow section formed in the bumper for example (see FIG. 49 of JP-A-6-171441). However, with these expanded elastomers, a relatively flat characteristics curve is observed in a graph representing the relationship of load and the level of displacement when impact load is input, so while energy absorption efficiency is relatively good, there is the problem of appreciable collapse residuum and poor space efficiency.
The other class is a rib structure formed from PP, PE (polyethylene), ABS resin or the like. This rib structure absorbs energy by means of a rib positioned so as to extent in the direction of input of impact, and that undergoes bucking deformation during impact input. However, this rib structure has the problem that, since typically the initial impact load tends to be high, the impact on the impacted object will tend to be high. Also, since the rib structure is manufactured by means of injection molding, manufacturing costs for elongated materials will tend to be high.
With the foregoing in view, as a result of successful development of an automotive impact-absorbing member that upon input of low impact load exhibits good impact energy absorbing function and that can advantageously protect the human body, the inventors has been developed an automotive impact-absorbing member comprising tabular ribs of resin positioned so as to extend in the direction orthogonal to the impact load input direction; and a pair of plate holding parts connected respectively at a first end thereof to the two ends of the tabular ribs and disposed on the diagonal so as to approach one another at increasing distance away from the first end in the direction perpendicular to the tabular ribs, and functioning to induce tensile deformation of the tabular ribs during impact load input. This prior invention of the present inventors has been filed in Japanese Patent Office as Japanese Patent Application, and not yet laid open on the priority date of this application. This automotive impact-absorbing member is used by being mounted on the bumper etc. installed at the front and back of an automobile, and can effectively protect pedestrians.
The automotive impact-absorbing member discussed above, for use in an automobile bumper, is typically formed as an elongated tube of resin mounted on the automobile bumper so that the impact-absorbing member extends in the lateral direction. When an automobile on which the impact-absorbing member has been mounted in this way has a mild collision with a pedestrian at low speed, for reasons relating to the mounting location of the impact-absorbing member, it will in many cases hit the pedestrian's legs, and the pattern of impact against the impact-absorbing member tends to be various as well. Consequently, in the event of impact with a pedestrian's legs, relatively low impact load will be input in one portion of the impact-absorbing member in the lateral direction, and thus it is not always the case that impact occurs in such a way that the impact load is input over the entire impact-absorbing member. As a result of testing of an impact-absorbing member for use in protecting the legs of pedestrians, the inventors found that during deformation of the impact-absorbing member produced by impact, load tends to be excessively high in the rear half from the center.